Trailers used in the medium and heavy duty trucking market are frequently equipped with liftgates that can lower/raise freight to/from the ground. Liftgate motors are powered by an auxiliary battery at the vehicle trailer that receives electrical power to be maintained in a charged state. The auxiliary battery is typically powered from the vehicle's battery or alternator via a junction box on the front of the trailer. The typical output of a tractor alternator is approximately 14 VDC, however, the voltage available at the junction box may generally be no higher than approximately 12.5 VDC. The voltage drop may, for example, be due to the length of a multi-pole connector connecting the electrical system of the tractor to the trailer junction box, which may be about 15 m to about 20 m. In the event that the tractor battery is running low, the voltage at the junction box of the trailer may be even lower than 12.5 VDC, which may be insufficient for fully charging the auxiliary battery at the trailer.